CRT04106 Radiation Sciences

DIAGNOSTIC RADIOGRAPHY · NTA LEVEL 4 · SEMESTER ONE Atomic Structure CRT04106 · Radiation Sciences START READING NOTES Study Atomic Structure using the sections below. Use the topic navigation to continue through Radiation Sciences. Contents of This Topic RELATED TASK ATOMIC STRUCTURE. NUCLEUS. Shell Types of Electrons Key points Atom Isotopes Periodic table Electronic configuration Bohr’s atomic theory Introduction RELATED TASK Describe atomic structure, quantities and units of electro-magnetic radiations, x-ray and gamma rays, primary and secondary radiation. ATOMIC STRUCTURE. Atom is the smallest unit of matter that define the chemical element. Atom made up of two main parts, that are, Nucleus: contains positive protons (p) and neutral neutrons (n) Shells: Contain electrons (e) that circles the nucleus in their energy level. NUCLEUS. Nucleus is the central part of an atom where almost the mass of an atom is present. Nucleus is composed of two main particles. Proton Neutron Protons are positively charged particle present in nucleus. Proton have a mass of 1.6726×10−27 kg. That is, they weigh 1,836 times the mass of electrons. Nucleus Neutrons are charge less particle present in a nucleus of an atom. Neutron have a mass of 1.6929×10−27 kg. that is, they weigh 1,839 times mass of electrons Both protons and neutrons in a nucleus of an atom are called Nucleons. Nucleus The number of protons present in nucleus of an atom is called Atomic number. And is denoted by a letter ‘Z’. The total number of protons and neutron in a nucleus of an atom is called Mass number. And is denoted by a letter ‘A’. Shell Shell is an orbit that consist of an electron(s) which evolves around the nuclear of an atom. Shell are also known as Energy level. Electron is negatively charged particle that revolves on its orbit around the nucleus. Electron has a mass of 9.11×10−31 kg. Each shell (orbit) has its maximum carrying capacity of electron. Shell The capacity of shell to carry the electrons is determined by the formula. 2n2 where n is the number (position) of shell from nuclear. The number of shells are numbered from the inner most shell to outer ward from the nuclear. The inner most shell are numbered as one (n=1) and others are continuously numbered in a sequence. Shells are also named as K, L, M, N Shell Types of Electrons Electrons are either bound or free. Bound electrons: These are the electrons that are held in orbit around the nucleus in the electron shells by the attractive force of the positive nucleus. The binding energy is the positive energy required to overcome the pull of the nucleus and release the electron from the shell. Types of Electrons Free electrons: These are the electrons that are not bound in an electron shell around a nucleus. They have a kinetic energy of: Kinetic energy = ½mv2 where: m = mass, v = velocity The actual binding energy of electrons is expressed in electron volts (eV) or keV (1keV = 1000 eV) 1 eV = 1.6022 x 10 -19 joules Free electron Key points Increase in the atomic number = increase in the binding energy of the electrons (there are more protons and, therefore, more energy is needed to release the electrons from the greater positive pull) Increase in the distance between the nucleus and the electron = decrease in the binding energy of the electron (decrease in the positive pull of the protons in the nucleus) Atom The number of the proton and electron in an atom is equal, thus, this make the atom to be electrically neutral. If either number of proton or electron exceed in an atom, it become electrically charged and is called an Ion. If proton exceed electron it become positively charged. And the atom is named Cation. And if electron exceed it become negatively charged. And the atom is named Anion. Atom Atom The number of proton in an atom determine it’s chemical element properties since each element has it’s own number of proton. For example hydrogen atom has only one proton in its nucleus, while Sodium atom has eleven protons in its nucleus. If the number of proton changed in the nucleus of an atom that atom changes its chemical element properties. Atom Atom of an element become charged by either losing or gaining electron on its outer most shells. Atom if gain extra electron it become negatively charged. And if loses the electron it become positively charged. The process of either gaining or losing of electron in an atom is called Ionization. Ionization Atom The atom of the same chemical element is said to have the same number of neutrons in its nucleus. But there are occasion where the number of neutrons in atom of the same chemical element differs. If the number of neutrons in atoms of the same chemical element differs these atoms are called Isotopes Isotopes Isotope are atoms of the same chemical element but different number of neutrons in its nucleus. Isotope Atomic Structure Isotones are atoms (nuclides) having the same number of neutrons but differ proton number. Example boron-12 and carbon 13 both contain 7 neutrons. Isobars are atoms (nuclides) of different chemical elements having the same atomic mass (number of nucleons). Example 40Ar, 40K and 40Ca. Isobars Isotones Periodic table The periodic table is a tabular arrangement of the chemical elements, organized on the basis of their atomic number, electron configurations, and recurring chemical properties. Elements are presented in order of increasing atomic number, which is typically listed with the chemical symbol in each box. Periodic table The standard form of the table consists of a grid of elements laid out in 18 columns and 7 rows, with a double row of elements below that. The table can also be deconstructed into four rectangular blocks: the s-block to the left, the p-block to the right, the d-block in the middle, and the f-block below that. Periods: Are rows of the table Groups: Are the columns of the table Periodic

DIAGNOSTIC RADIOGRAPHY · NTA LEVEL 4 CRT04106 Radiation Sciences Notes Browse 27 study topics in Radiation Sciences, NTA Level 4, Semester 1. Atomic Structure and Electromagnetic Radiation Radiation Sciences: Fundamental Concepts Radioactivity and X-ray Interaction with Matter X-rays production Radiation Effects in Body Tissues Characteristics Of Ioning Radiation In Tissue Characteristics Of Ionizing Radiation In Tissue X-ray Production, Spectrum and Radiation Protection Image Characteristics Radiation Monitoring Mechanisms of Radiation Damage Radiation Protection Dosimetry Principles X-ray Radiation Atomic Structure Basic Interactions Between X-Rays And Matter Body Habitus Control Of Scatter Radiation Determinants Of Biological Effects Dosimetry Principle Electromagnetic Radiation Factors Affecting Radiation Effect To Cell Quantities Of Dosimetry Radiation Propagation In Tissues Radiation Sciences 4.2.1 Radiation Units and protection Scatter Radiation ← PREVIOUS MODULENEXT MODULE →SEMESTER NOTESNTA LEVEL 4 NOTESALL NOTES Need These Notes as PDF? Need a clean, well-formatted PDF copy for offline study, revision or printing? Request the complete notes directly through WhatsApp. GET WELL-FORMATTED PDF NOTES

DIAGNOSTIC RADIOGRAPHY · NTA LEVEL 4 · SEMESTER ONE Scatter Radiation CRT04106 · Radiation Sciences START READING NOTES Study Scatter Radiation using the sections below. Use the topic navigation to continue through Radiation Sciences. Contents of This Topic INTRODUCTION Scattered x-rays cannot be completely removed by the use of anti scatter grids or energy filters. Sources of scatter radiation Characteristics of scatter radiation Effects of scatter radiation Solution to Decrease of scatter radiation Beam Limiting devices Compression technique in mammography Air gap technique Radiographic grids Filtration Other methods to decrease scatter Optimizing Technical Parameters Secondary Protective Barriers and Apparel Scatter Radiation Reduction of Repeat Examinations Scatter Radiation INTRODUCTION When a photon beam interacts with matter, some of its part get absorbed, some gets deflected to new direction and rest of it is transmitted to produce a radiographic image. The part which is deflected from its original path to a new direction is known as scatter radiation. The secondary radiation which makes no favorable contribution to the formation of image and produce an overall blackness on the film thus reducing the image contrast. Scattered x-rays cannot be completely removed by the use of anti scatter grids or energy filters. Scatter radiation is a result of either coherent scattering or the Compton effect Some scattering also occurs as a result of interaction between the x-ray beam and the tabletop and image receptor (IR), and any other matter that happens to be within the radiation field. Sources of scatter radiation Patient him/herself Glass walls of x-ray tube Tabletop Cassette Back scatter from floor Back scatter from wall Characteristics of scatter radiation More oblique in nature Produced by matter in all directions Less energy than primary beam With increase in energy of primary radiation more scatter produced Amount of scatter depends on Volume of tissue Thickness of patient KVp used Effects of scatter radiation Increase overall density of the film which is not useful in production of image thus produces fog Reduces contrast Reduce light transmitting ability of film/cassette Result in formation of noise Solution to Decrease of scatter radiation Beam limiting devices ( collimation) Filtration Radiographic grids Air gap technique Compression in mammography Beam Limiting devices In addition to decreasing patient dose, beam limiting devices such as collimators reduce the amount of scatter radiation and thereby increasing image contrast. Collimation refers to decreasing the size of the projected field to limit the x-ray beam field size to the anatomic area of interest only. Beam restriction serves two purposes: Limiting patient exposure Reducing the amount of scatter radiation produced within the patient. Compression technique in mammography It reduces amount of scatter by diminishing the thickness of tissue through which x-rays pass through. It displaces the adipose tissue sideways thus reducing the volume of the part to be x-rayed and lowers the kilovoltage to be used Advantages It acts as immobilizing device Helps in the reduction of the scatter radiation thus improving the contrast. Air gap technique The air gap technique is a scatter reduction method that uses an increased object to image distance to reduce scatter reaching the image receptor. This technique is used in lateral C- Spine and chest radiographs. Since the patient is the source of scatter and the increased object to image receptor distance causes much of the scattered radiation to miss the image receptor. This reduces scatter and improve the contrast of the image. The major disadvantage of the air gap technique is the loss of sharpness which results from the increased object to image receptor distance. Radiographic grids It is a radiographic accessory which is designed to minimize the effect of scatter radiation reaching the film. A radiographic grid is a device made of parallel radiopaque strips alternately separated with low-attenuation strips of Aluminum, Plastic and Wood. It is placed between the patient and the radiographic image receptor to remove scattered x-ray photons that emerge from the patient before they reach the film or other image receptor. Improves image contrast significantly.. Filtration This is the process of shaping the x-ray beam to increase the amount of useful photons and decrease the low energy photons. When x-ray photons interact with the human body only the high energy photons penetrate the body, while low energy photons are absorbed in the body and contribute to scatter. Filtration absorbs the low energy photons from the beam and hence increases the image contrast. Other methods to decrease scatter Optimizing Technical Parameters Secondary Protective Barriers and Apparel Reduction of Repeat Examinations Optimizing Technical Parameters KVp Affects the penetrability of the beam Higher kVp, more photons go through patient to the Image receptor, less absorbed by patient, higher scatter and less contrast on image Lower the kVp, increase in dose absorbed by patient, less fog on film more contrast image Higher kVp and lower mA reduce the overall number of photons, decreasing scatter generation. Secondary Protective Barriers and Apparel Secondary protective barriers, such as lead-lined walls and ceilings, shield individuals from scattered and leakage radiation. Protective apparel, including lead aprons, gloves, and thyroid shields, ensures the safety of personnel and patients during radiographic procedures. These measures are particularly important in high-scatter environments like fluoroscopy suites. Scatter Radiation To reduce scatter radiation during C-arm fluoroscopy, position the C-arm so that the x-ray tube is under the patient whenever possible. Reduction of Repeat Examinations Unnecessary repeats not only increase patient dose but also result in additional scatter. Ensuring proper technique, patient positioning, and equipment calibration reduces the likelihood of retakes, contributing to lower overall scatter levels. ← PREVIOUS TOPICVIEW ALL MODULE NOTESVIEW SEMESTER NOTESVIEW ALL LEVEL NOTESALL DIAGNOSTIC RADIOLOGY NOTES Need These Notes as PDF? 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DIAGNOSTIC RADIOGRAPHY · NTA LEVEL 4 · SEMESTER ONE Radiation Units and protection CRT04106 · Radiation Sciences START READING NOTES Study Radiation Units and protection using the sections below. Use the topic navigation to continue through Radiation Sciences. Contents of This Topic Radiation Units Introduction Radiation Activity Radiation exposure Absorbed dose Equivalent dose Effective dose Radiation Protection Radiation Safety ALARA Vs ALADA Radiation Units and protection Designation of special areas Radiation Units Radiation Protection Introduction Determination of the energy imparted to matter by radiation is the main subject of Dosimetry. The imparted energy is responsible for the effects that radiation causes in matter, for instance, a rise in temperature, or chemical or physical changes in the material properties. Several of the changes produced in matter by radiation are proportional to the absorbed dose, giving rise to the possibility of using the dosimeter material sensitive part to measure absorbed dose. Introduction Radiation discussion involves the measure of two phenomena which are activity and exposure. Activity is basically just how much radiation is coming out of the material, whether it's particles or waves i.e. The rate of disintegration of a radioactive material. Exposure measures the effect of radiation on substances that absorb it. Radiation Activity Radiation activity is measured in an international (SI) unit called a Becquerel (Bq). The Becquerel counts how many particles or photons (in the case of wave radiation) are emitted per second by a source. Radiation exposure Radiation exposure is expressed in several ways to account for the different levels of harm caused by different forms of radiation and the different sensitivity of body tissues. Measurement of the ionization produced by radiation is the first choice used to quantify the passage of radiation through matter. Radiation exposure Radiation exposure is a measure of the ionization of air due to ionizing radiation from high-energy photons (i.e. X-rays and gamma rays). Radiation exposure is defined as the sum of electrical charges (∆q) on all the ions of one sign produced in air when all the electrons, liberated by photons in a volume of air whose mass is ∆m, are completely stopped in air. Radiation exposure Radiation exposure is given the symbol X. The SI unit of radiation exposure is the coulomb per kilogram (C/kg), but in practice, the roentgen is used. The roentgen, abbreviated R, is the unit of radiation exposure. In the original definition 1 R means the amount of X-rays or γ-radiation that is required to liberate positive and negative charges of one electrostatic unit of charge in 1 cm³ of dry air at (STP) Radiation exposure one roentgen corresponds to 2.58 x 10-4 coulomb per kg of ions generated in air. The calculation of radiation dose (in Gy) from a radiation exposure of 1 R depends on the energy of the X-rays or γ-rays and the composition of the irradiated material. For example, if soft tissue is exposed to γ-rays of 1 R, the radiation dose will be approximately 9.3 milligray (mGy) Absorbed dose Dose is defined as the amount of energy deposited by ionizing radiation in a substance. For a given radiation field, the absorbed dose will depend on the type of matter which absorbs the radiation. Although a large number of possible interactions are known, there are three key interaction mechanisms of gamma rays with matter Photoelectric effect Compton scattering Pair production Absorbed dose Absorbed dose is the radiation energy deposited per unit mass of the material. The definition of absorbed dose is the quotient dE/dm. where dE is the mean energy imparted by ionizing radiation to material of mass dm. The quantity absorbed dose has been defined to describe the quantity of radiation for all types of ionizing radiation, including charged and uncharged particles; all material; and all energy. Absorbed dose Absorbed dose is a measure of the biologically significant effects produced by ionizing radiation. The old unit of absorbed dose is RAD (an acronym for “radiation absorbed dose”) and represent the absorption of 100ergs of energy per gram of absorbing material. 1 rad = 100 ergs/g = 10-2J/Kg Absorbed dose The SI unit for absorbed dose is Gray (Gy) and is defined as 1Gy = 1 J/Kg Thus, the relationship between Gray, cent gray and rad is 1Gy = 100rad = 100cGy. Equivalent dose Because the biologic effects of radiation depend not only on dose, but also on the type of radiation, the dosimetry quantity relevant to radiation protection is the dose equivalent (H). It is defined as H = D.Q Where D is the absorbed dose and Q is the quality factor for the radiation. Equivalent dose Equivalent dose = absorbed Dose multiplied the appropriate radiation weighting factor. The radiation weighting factors are needed because different types of radiation (like alpha, beta, gamma, and neutrons) can have different effects even if the absorbed dose is the same. Weighting factors Equivalent dose Equivalent dose is expressed in sieverts (Sv), or, more frequently, millisieverts (mSv) which are 1/1000th of a sievert, and the organ should always be specified (for example "25 mSv to the skin"). In the simplest cases, for gamma (photon) and beta (electron) radiation, the radiation weighting factor is 1, and therefore, for example, an absorbed dose of 1 mGy in an organ equals an equivalent dose of 1 mSv to that organ. Equivalent dose The SI unit for both dose and dose equivalent is Joules per kilogram, but the special name for the SI unit of dose equivalent is SIEVERT (Sv). 1Sv = 1 J/Kg. The older unit of dose equivalent is REM 1rem = 10-2Sv Equivalent dose Equivalent dose is calculated for individual organs. It is based on the absorbed dose to an organ, adjusted to account for the effectiveness of the type of radiation. Equivalent dose is expressed in millisieverts (mSv) to an organ. The use of quality factor in radiation protection is analogous to the use of relative biologic effectiveness (RBE) in radiation biology. Effective dose Whole-body exposures are rarely uniform For a given exposure received, internally

DIAGNOSTIC RADIOGRAPHY · NTA LEVEL 4 · SEMESTER ONE Radiation Sciences 4.2.1 CRT04106 · Radiation Sciences START READING NOTES Study Radiation Sciences 4.2.1 using the sections below. Use the topic navigation to continue through Radiation Sciences. Contents of This Topic Objectives X-RAY TUBE Additional components The function of the X-ray tube is to: Radiation Sciences 4.2.1 TUBE HOUSING Electrical Insulation: Prevents high-voltage electrical leakage. SHIELDING CATHODE Functions: ANODE Materials in Anode: Why Tungsten for Target? TUBE COOLING GENERATION OF X-RAYS Below is a step-by-step explanation of how X-rays are generated: 2. Acceleration of Electrons 3. Electron-Anode Interaction b) Characteristic Radiation 4. X-ray Beam Formation 5. Energy Distribution FACTORS AFFECTING THE QUALITY OF X-RAY GENERATED 1. Tube Voltage (kVp – Kilovoltage Peak) 2. Tube Current (mA – Milliamperage) 3. Exposure Time (s) 4. Filament Temperature 5. Focal Spot Size 6. Target Material (Anode Composition) 7. Anode Angle 8. Anode Rotation Speed (for Rotating Anodes) 9. Filtration 10. Tube Cooling System 11. Beam Collimation and Alignment 12. Vacuum Quality in the Tube PATIENT CONDITION IN DECIDING EXPOSURE TYPE AND DOSE 1. Patient Size and Body Composition Exposure Type: Use low-dose settings to minimize radiation exposure. b) Obese Patients 2. Pathological Conditions COPD (decreased lung density): b) Bone Imaging (e.g., Osteoporosis, Fractures) 3. Age and Sensitivity b) Pregnant Patients 4. Imaging Region and Type of Examination b) Abdominal X-ray c) Extremity X-ray (e.g., hands, feet) 5. Use of Contrast Media RADIATION SCIENCES Objectives At the end of this session students must be able to; Describe X-ray tube, tube housing, shielding, anode, cathode and tube cooling. Describe generation of X-rays and factors affecting its quality. Demonstrate patient condition in deciding exposure type and dose. X-RAY TUBE The X-ray tube is the core component of the X-ray system, where X-rays are generated. It is a vacuum-sealed device that accelerates electrons from the cathode to the anode, producing X-rays through the interaction of electrons with the anode material. X-RAY TUBE The x-ray tube contains two principal elements: Filament (Cathode): boils off electrons Target (Anode): electrons strike to produce x-rays Additional components Expansion bellows (provide space for oil to expand) Tube envelope (evacuated) Tube housing Cooling dielectric oil Rotor Induction stator Tube window: usually made from beryllium, not glass The function of the X-ray tube is to: Provide a beam of X-rays from as near a point source as possible (focus). Dissipate the heat produced effectively to prevent damage to the X-ray tube (approximately 99 per cent of the energy conversions produce heat). Provide a consistent quality (kVp) and quantity (mAs) of radiation Radiation Sciences 4.2.1 Allow X-rays to emerge only from the window (port) of the housing of the tube and exclude emissions from elsewhere in the housing, which is lined with lead sheet. Provide an electrically safe environment for the practitioner. The tube is securely supported, but capable of easy movement into any position and then being maintained in that position. TUBE HOUSING TUBE HOUSING Is the portion of an x-ray system which contains the x-ray tube and/or secondary target. TUBE HOUSING The tube housing encloses the X-ray tube and serves several key functions: Radiation Shielding: Made of lead-lined material to prevent stray X-rays from escaping. Mechanical Protection: Protects the fragile X-ray tube from external damage. Electrical Insulation: Prevents high-voltage electrical leakage. Heat Dissipation: Contains cooling systems to manage heat generated during operation. SHIELDING External Shielding: Lead lining in the tube housing minimizes exposure to stray radiation. Internal Shielding: Filters may be placed to remove low-energy, non-useful X-rays, reducing patient exposure. Collimators: Further limit the beam to the desired area, enhancing safety and image quality. CATHODE The cathode emits electrons through thermionic emission when heated. It consists of: Filament: A coiled wire (usually tungsten) that produces electrons when heated. Focusing Cup: Negatively charged to direct and focus the electron beam toward the anode. Functions: Provides a source of electrons needed for X-ray production. Shapes and focuses the electron stream for efficient X-ray generation. ANODE The anode is the target where high-speed electrons collide, producing X-rays. It can be: Stationary Anode: Used in low-power X-ray systems (e.g., dental X-rays). Rotating Anode: Used in high-power systems for improved heat dissipation. STATIONARY AND ROTATING ANODE Materials in Anode: Tungsten: High atomic number and melting point, making it ideal for X-ray production. Molybdenum or Copper: Sometimes used as a base for the rotating anode. Why Tungsten for Target? Atomic number -Tungsten’s high atomic number, 74, results in high-efficiency x-ray production and in high-energy x-rays. Thermal conductivity -Tungsten has a thermal conductivity nearly equal to that of copper. It is therefore an efficient metal for dissipating the heat produced. High melting point, Any material, if heated sufficiently, will melt and become liquid. Tungsten has a high melting point (3400°C compared with 1100°C for copper) and therefore can stand up under high tube current without pitting or bubbling. Functions: Converts kinetic energy of electrons into X-rays (about 1% efficiency). Dissipates heat generated during the process. TUBE COOLING Cooling is essential due to the immense heat generated during X-ray production. Methods include: Oil Cooling: Oil surrounds the tube to absorb and transfer heat away from the X-ray tube. Air Cooling: Fans circulate air around the housing to dissipate heat. Rotating Anode: Distributes heat over a larger surface area, increasing thermal efficiency. Water Cooling: Used in high-end systems for superior heat removal. GENERATION OF X-RAYS X-rays are produced when high-speed electrons collide with a metal target (anode) in an X-ray tube. The process involves the conversion of kinetic energy of electrons into electromagnetic radiation. Below is a step-by-step explanation of how X-rays are generated: Electron Production (Thermionic Emission) Cathode: The cathode contains a filament (usually tungsten) that is heated by an electrical current. Electron Emission: When heated, the filament releases electrons through thermionic emission, where the thermal energy overcomes the binding energy of electrons. 2. Acceleration of Electrons High Voltage (kVp): A high voltage is applied between the cathode (negative) and anode (positive), creating a strong electric field. Electron Acceleration: The electrons

DIAGNOSTIC RADIOGRAPHY · NTA LEVEL 4 · SEMESTER ONE Radiation Propagation In Tissues CRT04106 · Radiation Sciences START READING NOTES Study Radiation Propagation In Tissues using the sections below. Use the topic navigation to continue through Radiation Sciences. Contents of This Topic RADIATION PROPAGATION IN TISSUES INTRODUCTION Overview of ProcesSES: Fundamentals of Radiation-Tissue Interaction Characteristics of Body Tissues Affecting Radiation Interaction: Composition The interaction of radiation with different tissue types is the basis for creating contrast in medical images. Radiation Absorption Mechanisms of Absorption: Pair Production (High Energy) Factors Influencing Absorption Radiation absorption forms the basis for contrast in X-ray images Radiation Transmission Significance in Imaging: Factors Influencing Transmission Composition of Tissue: Transmission plays a key role in creating contrast in radiographic images. Radiation Scattering Key Types of Scattering: Compton Scattering: Coherent (Rayleigh) Scattering Impact on Medical Imaging: Impact of scattering on Radiation Safety Minimizing Scattering in Imaging: Radiation Reflection Reflection is more significant for non-ionizing radiation, such as ultrasound, where sound waves reflect at tissue interfaces. Mechanism of Reflection: Applications of reflection in Medical Imaging: Reflection in Ionizing Radiation Minimizing Reflection Artifacts: Comparison of Processes Factors Influencing Radiation Propagation Factor RADIATION PROPAGATION IN TISSUES RADIATION SCIENCES INTRODUCTION Radiation propagation in body tissues refers to how radiation interacts with and travels through the body's biological structures. This process is central to understanding how medical imaging and therapeutic techniques work. Overview of ProcesSES: Absorption -Radiation energy is absorbed by tissue, contributing to image contrast in modalities like X-rays and CT. Transmission Radiation passes through tissue without interaction, creating dark areas in images, such as air-filled spaces. Scattering -Radiation is deflected within tissues, which can degrade image quality and increase radiation dose to healthcare workers. Reflection Radiation is redirected at tissue interfaces, more relevant in ultrasound and non-ionizing radiation applications. Fundamentals of Radiation-Tissue Interaction Nature of Ionizing Radiation: -Ionizing radiation includes high-energy particles or waves like X-rays and gamma rays. -These forms of radiation have enough energy to ionize atoms by removing electrons. Characteristics of Body Tissues Affecting Radiation Interaction: Density -Denser tissues, such as bone, absorb more radiation compared to softer tissues like muscle or fat. Atomic Number (Z) -Higher atomic number tissues (e.g., bone with calcium) have a higher likelihood of absorbing radiation via the photoelectric effect. Composition -The chemical and physical makeup of tissues determines how they interact with radiation (e.g., fat vs. water content). The interaction of radiation with different tissue types is the basis for creating contrast in medical images. For instance: Bones (high Z) absorb more radiation, appearing bright on X-rays. Lungs (air-filled) allow more transmission, appearing dark on X-rays Radiation Absorption Radiation absorption refers to the transfer of energy from ionizing radiation (e.g., X-rays, gamma rays) to the atoms or molecules in tissue. This process results in ionization or excitation of atoms, leading to energy deposition in tissue. Mechanisms of Absorption: Photoelectric Effect: -Dominates at lower photon energies and in tissues with higher atomic numbers (e.g., bone). =The photon is completely absorbed, and an electron is ejected from the inner shell of an atom. -This creates image contrast in X-ray and CT imaging. Pair Production (High Energy) -Occurs at very high photon energies (above 1.02 MeV). -Photon energy converts into an electron-positron pair (not common in diagnostic imaging). Factors Influencing Absorption Energy of Radiation: Lower-energy photons are more likely to be absorbed (e.g., photoelectric effect). ii. Tissue Atomic Number (Z): Tissues with higher Z (e.g., calcium in bone) absorb more radiation. iv. Tissue Thickness and Density: Thicker and denser tissues result in greater absorption. The way radiation is absorbed, transmitted, scattered, or reflected depends on tissue characteristics and radiation energy. Radiation absorption forms the basis for contrast in X-ray images -High Absorption Areas (Bright): Bone and calcifications. Low Absorption Areas (Dark): Air-filled structures like lungs. Radiation Transmission Radiation transmission occurs when radiation passes through tissue without interacting with its atoms or molecules. This process allows the radiation to continue its path, reaching the detector or image receptor. Significance in Imaging: -Areas where radiation transmits freely appear darker on imaging modalities like X-rays or CT scans. -Examples: Air-filled structures such as lungs or bowel. Low-density tissues like fat. Factors Influencing Transmission Energy of Radiation: High-energy photons are more likely to transmit through tissues without interaction. Tissue Thickness and Density: Thinner or less dense tissues allow greater transmission. Dense tissues (e.g., bone) block transmission, contributing to image contrast. Composition of Tissue: Tissues with low atomic numbers (e.g., soft tissue) transmit more radiation compared to those with high atomic numbers. Transmission plays a key role in creating contrast in radiographic images. The balance between transmitted and absorbed radiation defines the light and dark regions on the image. Radiation Propagation In Tissues In diagnostic imaging, proper calibration of radiation energy is essential to optimize transmission, ensuring sufficient detail in images while minimizing patient exposure. Excessive transmission through dense tissues can reduce diagnostic value, necessitating adjustments in imaging parameters. Radiation Scattering Radiation scattering occurs when a photon interacts with tissue and is deflected from its original path.This process changes the direction of the radiation without complete absorption. Key Types of Scattering: Compton Scattering Coherent (Rayleigh) Scattering Compton Scattering: Dominates in soft tissues and at medium to high photon energies. A photon interacts with an outer-shell electron, resulting in: Ejection of the electron. Scattered photon with reduced energy. Responsible for image degradation and scatter radiation exposure Coherent (Rayleigh) Scattering -Occurs at low photon energies. -Photon changes direction without energy loss. -Minimal impact on diagnostic imaging Impact on Medical Imaging: Image Quality: Scattered radiation contributes to background "noise," reducing image contrast and detail. Artifacts: Increased scattering can lead to imaging artifacts, especially in thick or dense body regions. Impact of scattering on Radiation Safety Scattered Radiation Exposure: Scattered photons can escape the patient’s body, posing a risk to healthcare workers. This is a major concern in interventional radiology and fluoroscopy Minimizing Scattering in Imaging: Use of Grids: -Grids in X-ray machines filter out scattered photons before they reach the detector. Collimation:

DIAGNOSTIC RADIOGRAPHY · NTA LEVEL 4 · SEMESTER ONE Quantities Of Dosimetry CRT04106 · Radiation Sciences START READING NOTES Study Quantities Of Dosimetry using the sections below. Use the topic navigation to continue through Radiation Sciences. Contents of This Topic USE OF RADIATION EFFECT IN BODY TISSUES SKILLS IN DETERMINING EXPOSURES DOSE TO PATIENT (QUANTITIES RELATED TO DOSIMETRY) Quantities Related to Dosimetry E- Mean energy imparted to matter of mass m Apart from Gy, there is another unit of absorbed dose called rad. Imparted energy Equivalent Dose When it comes to the effects of radiation, one can not use absorbed dose as the relevant quantity. Equivalent dose is the product of absorbed dose received by tissue (T) from radiation (R) and radiation weighting factor HT.R s the equivalent dose due to radiation type R, Quantities Of Dosimetry The equivalent doses due to γ-rays and neutrons are given by EFFECTIVE DOSE The tissue weighting factor for stomach is WT = 0.12 as given in Table KERMA USE OF RADIATION EFFECT IN BODY TISSUES SKILLS IN DETERMINING EXPOSURES DOSE TO PATIENT (QUANTITIES RELATED TO DOSIMETRY) RADIATION SCIENCES Quantities Related to Dosimetry Radiation Exposure and Dose Roentgen (R) Absorbed Dose Equivalent Dose Effective Dose Flux or Fluence Rate Integrated Flux or Fluence Kerma, Cema, and Terma ABSORBED DOSE E- Mean energy imparted to matter of mass m Unit: SI unit= Gray 100 rads=1 Gy Old unit=Rads 1 Gy= 1J/kg Apart from Gy, there is another unit of absorbed dose called rad. Even though rad has mostly been replaced by Gy it is still found in some modern literature. Rad was introduced in 1953 to replace Roentgen, which was the unit of exposure due to x-rays or γ-rays only. It is defined as the dose equivalent to the absorption of 0.01 joule of energy per kilogram of tissue Imparted energy It is the total amount of energy deposited in matter It is the product of dose & mass over which the energy is imparted Unit: J Equivalent Dose Absorbed dose is not capable of characterizing the biological effect of radiation Absorbed dose is not capable of characterizing damage to any medium All it tells us is how much energy has been absorbed by the medium and not what this deposited energy has done to the medium For this case of absorbed dose, there is no difference between a photon and an α-particle if they deposit the same amount of energy. When it comes to the effects of radiation, one can not use absorbed dose as the relevant quantity. Since dosimetry is primarily concerned with the safety of personnel, therefore a quantity called equivalent dose has been defined that characterizes the damaging effect of radiation on tissue Equivalent dose is the product of absorbed dose received by tissue (T) from radiation (R) and radiation weighting factor It is denoted by HT.R HT.R= DTR X WR WR= Radiation weighting factor Formely called quality factor basically defines the quality of the radiation that is interacting with the matter Quality of a radiation depends upon two parameters LET & RBE HT.R s the equivalent dose due to radiation type R, DTR is the mean absorbed dose delivered by radiation R, and WR is the radiation weighting factor. The radiation weighting factor is given by WR = QR · NR where QR and NR are the quality and modified factors for the radiation type R respectively Quantities Of Dosimetry In case of mixed field, the total equivalent dose can be obtained by simply summing the contribution due to individual types of radiation, that is HT = R wR · DTR. Quantities Of Dosimetry Example: In a mixed radiation environment, a person receives 20 mGy of γ-ray dose and 2 mGy of slow neutron dose. Calculate the total equivalent dose received by the person. Solution As the source is external, we can take NR = 1 and the weighting factors for the two radiation types as given as wγ = 1 and wn = 5. The equivalent doses due to γ-rays and neutrons are given by HT,γ = wγ · DT,γ = (1)(20) = 20 mSv HT,n = wn · DT,n = (5)(2) = 10 mSv The total dose received by the person is then sum of these individual doses, that is HT = HT,γ + HT,n = 20 + 10 = 30 mSv EFFECTIVE DOSE The equivalent dose as described above can be used for one tissue type only as it does not address the sensitiveness of tissue types to the same type of radiation. The question is, how we can determine the whole body equivalent dose to estimate the risk associated with a certain type of radiation environment?. Or how one can estimate the whole body dose if the dose received by a particular organ is known. This is done by using the quantity effective dose Effective dose Can be defined as the product of equivalent dose and tissue weighting factor Since all tissues doesn’t have the same sensitivity towards radiation, so each tissue is given a factor based on the response to radiation This factor is called tissue weighting factor It is denoted by E E=Sum(HTR X WT) WT= Tissue weighting factor Unit= SI unit= Sievert (Sv) Quantities Of Dosimetry Example: During a CT scan of the stomach, that had to be repeated several times, a patient receives a total absorbed dose of 0.3 Gy. Compute the total effective dose received by the patient. Solution Since CT scan is performed with x-rays therefore the radiation weighting factor WR = 1. The equivalent dose received by the patient’s stomach is HT,R = WR · DT,R = (1)(0.3) = 0.3 Sv The tissue weighting factor for stomach is WT = 0.12 as given in Table The effective dose is then give by E = WT · HT,R = (0.12)(0.3) = 0.036 Sv = 36 mSv. The usual effective dose received during a typical CT scan of abdomen is around 10 mSv, which means that this patient received more

DIAGNOSTIC RADIOGRAPHY · NTA LEVEL 4 · SEMESTER ONE Factors Affecting Radiation Effect To Cell CRT04106 · Radiation Sciences START READING NOTES Study Factors Affecting Radiation Effect To Cell using the sections below. Use the topic navigation to continue through Radiation Sciences. Contents of This Topic RADIATION CELL DAMAGE OBJECTIVES INTRODUCTION FACTORS WHICH MODIFY CELL DAMAGE BY RADIATION PHYSICAL FACTORS ii. Relative Biologic Effectiveness Factors Affecting Radiation Effect To Cell iii. Protraction and Fractionation BIOLOGIC FACTORS THAT AFFECT RADIOSENSITIVITY AND CELL DAMAGE Oxygen Effect ii. Age iii. Recovery If a tissue or organ receives a sufficient radiation dose, it responds by shrinking. CHEMICAL FACTORS Radiosensitizers ii. Radioprotectors. iii. Other molecules/water molecules RADIATION CELL DAMAGE RADIATION SCIENCE OBJECTIVES Understand definition of ionzing radiation Identify types radiation Highlight examples of ionizing radiation Explain direct and indirect mechanism of cell damage Understand how physical, chemical and biological factors contribute to cell damage by radiation INTRODUCTION What is ionizing radiation? Types of radiation Examples of ionizing radiation Explain direct and indirect mechanism of cell damage by radiation FACTORS WHICH MODIFY CELL DAMAGE BY RADIATION Physical factors Biological factors Chemical factors PHYSICAL FACTORS Linear energy transfer Relative biological effectiveness Protraction and fractionation PHYSICAL FACTORS LINEAR ENERGY RANSFER -Linear energy transfer (LET) is a measure of the rate at which energy is transferred from ionizing radiation to soft tissue -LET is expressed in units of kiloelectron volt of energy transferred per micrometer of track length in soft tissue (keV/µm). -The ability of ionizing radiation to produce a biologic response increases as the LET of radiation increases. When LET is high, ionizations occur frequently, increasing the probability of interaction with the target molecule The LET of diagnostic x-rays is approximately 3 keV/µm ii. Relative Biologic Effectiveness As the LET of radiation increases, the ability to produce biologic damage also increases. This effect is quantitatively described by the relative biologic effectiveness (RBE) Factors Affecting Radiation Effect To Cell Diagnostic x-rays have an RBE of 1. Whereas radiations with lower LET than diagnostic x-rays have an RBE less than 1, radiations with higher LET have a higher RBE. iii. Protraction and Fractionation -If a dose of radiation is delivered over a long period of time rather than quickly, the effect of that dose is less. -Stated differently, if the time of irradiation is lengthened, a higher dose is required to produce the same effect. This lengthening of time can be accomplished in two ways. If the dose is delivered continuously but at a lower dose rate, it is said to be protracted. Six gray (600 rad) delivered in 3 -minutes at a dose of 2 Gyt/min is lethal for a mouse. However, when 6 Gyt is delivered at the rate of 10 mGyt/hr for a total time of 600 hours, the mouse will survive. Factors Affecting Radiation Effect To Cell If the 6-Gyt dose is delivered at the same dose rate, but in 12 equal fractions of 500 mGyt, all separated by 24 hours, the mouse will survive. In this situation, the dose is said to be fractionated. Radiation dose fractionation reduces effect because cells undergo repair and recovery between doses. Dose fractionation is used routinely in radiation oncology. BIOLOGIC FACTORS THAT AFFECT RADIOSENSITIVITY AND CELL DAMAGE Oxygen effect Age Recovery Oxygen Effect -Tissue is more sensitive to radiation when irradiated in the oxygenated, or aerobic, state than when irradiated under anoxic (without oxygen) or hypoxic (low-oxygen) conditions. -This characteristic of tissue radiation response is called the oxygen effect and is described numerically by the oxygen enhancement ratio (OER). ii. Age -The age of a biologic structure affects its radiosensitivity. -The response of humans is characteristic of this age-related radiosensitivity -Humans are most sensitive before birth. -After birth, sensitivity decreases until maturity, at which time humans are most resistant to radiation effects. In old age, humans again become somewhat more radiosensitive. iii. Recovery -Human cells can recover from radiation damage. -If the radiation dose is not sufficient to kill the cell before its next division (interphase death), then given sufficient time, the cell will recover from the sublethal radiation damage it has sustained. -Some types of cells have greater capacity than others for repair of sublethal damage. -At the whole-body level, this recovery from radiation damage is assisted through repopulation by surviving cells If a tissue or organ receives a sufficient radiation dose, it responds by shrinking. This is called atrophy, and it occurs because some cells die and disintegrate and are carried away as waste products. If a sufficient number of cells sustain only sublethal damage and survive, they may proliferate and repopulate the irradiated tissue or organ CHEMICAL FACTORS Radiosensitizers Radioprotectors Free radicals/other molecules (water molecules) Radiosensitizers -Agents that enhance the effect of radiation are called sensitizing agents. Examples include halogenated pyrimidines, methotrexate, actinomycin D, hydroxyurea, and vitamin K. -The halogenated pyrimidines become incorporated into the DNA of the cell and amplify the effects of radiation on that molecule. All radiosensitizers have an effectiveness ratio of approximately 2, that is, if 90% of a cell culture is killed by 2 Gyt (200 rad), then in the presence of a sensitizing agent, only 1 Gyt (100 rad) is required for the same percentage of lethality ii. Radioprotectors. Radioprotective compounds include molecules that contain a sulfhydryl group (sulfur and hydrogen bound together), such as cysteine and cysteamine. Hundreds of others have been tested and found effective by a factor of approximately 2. For example, if 6 Gyt (600 rad) is a lethal dose to a mouse, then in the presence of a radioprotective agent, 12 Gyt (1200 rad) would be required to produce lethality iii. Other molecules/water molecules -Water molecules act as a medium for radiation-induced free radical generation, amplying damage through indirect mechanism ← PREVIOUS TOPICNEXT TOPIC →VIEW ALL MODULE NOTESVIEW SEMESTER NOTESVIEW ALL LEVEL NOTESALL DIAGNOSTIC RADIOLOGY NOTES Need These Notes as PDF? Need a clean, well-formatted PDF copy for offline study, revision or printing? Request the complete notes directly through WhatsApp. GET WELL-FORMATTED PDF NOTES

DIAGNOSTIC RADIOGRAPHY · NTA LEVEL 4 · SEMESTER ONE Electromagnetic Radiation CRT04106 · Radiation Sciences START READING NOTES Study Electromagnetic Radiation using the sections below. Use the topic navigation to continue through Radiation Sciences. Contents of This Topic Introduction Electromagnetic Waves Sine Wave Electromagnetic Spectrum Visible Radiation Wave-Particle Duality Types of EMR Uses of EMR Visible Light Electromagnetic Radiation Introduction Is the flow of energy at the universal speed of light through free space or through a material medium in the form of the electric and magnetic fields. Visible light is one type of electromagnetic radiation, other familiar forms are invisible electromagnetic radiations such as X-rays and radio waves. EMR consists of electromagnetic waves. Electromagnetic radiation is a type of energy that is all around us and takes many forms, such as radio waves, microwaves, X-rays and gamma-rays. Introduction Electromagnetic Waves Electromagnetic waves are waves oscillations of electric and magnetic fields that propagate at the speed of light. The oscillations of the two fields are perpendicular to each other and perpendicular to the direction of energy and wave propagation. The electric and magnetic fields in EMR waves are always in phase and at 90 degrees to each other. Electromagnetic Waves Electromagnetic Waves The electromagnetic radiation are distinguished by frequency and wave length of their electromagnetic wave. Frequency is the number of complete cycles formed by a wave at a period of a second. The SI unit of frequency is Hertz (Hz) but also can be expressed as per second. It is represented Electromagnetic Waves Wave length is the distance cover by a single complete cycle (frequency) of a wave. Wave length is the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings The unit of wave length is Meter (M). Wavelength is represented by lambda. Sine Wave Is a mathematical curve that describes a smooth repetitive oscillation. The sine wave is important in physics because it retains its wave shape when added to another sine wave of the same frequency and arbitrary phase and magnitude. It is the only periodic waveform that has this property. Electromagnetic waves are also a sine wave. Sine Wave Electromagnetic Spectrum Is the range separation of Electromagnetic radiation according to their frequency and wave length. The electromagnetic radiation classified as; radio waves, microwave, infrared rays, visible light, ultraviolet rays, X-rays and gamma rays. Although all electromagnetic waves travel at the speed of light in a vacuum, they do so at a wide range of frequencies, wavelengths, and photon energies. Electromagnetic Spectrum Visible Radiation Light is the most familiar form of electromagnetic radiation and makes up that portion of the spectrum to which the eye is sensitive. The corresponding wavelengths extend from 7 × 10-5 centimeter (red) to 4 × 10-5 centimeter (violet). Why visible radiation is important to our life?. Wave-Particle Duality Wave particle duality is the behavior of electromagnetic radiation that it exhibit both wave like nature and particle like nature. Electromagnetic radiation is usually thought of as being a wave. How is it known that it behaves like a wave? If visible light is considered, it can be demonstrated that visible light can undergo reflection, réfraction, diffraction, interference, etc., all of which are properties of waves. Wave-Particle Duality Particle – like properties Some phenomena associated with electromagnetic radiation, such as the photoelectric effect and Compton scattering, cannot be explained by the wave theory. To explain these phenomena, electromagnetic radiation must be considered to behave as particles or packets of energy rather than as waves. Wave-Particle Duality Wave-Particle Duality Electromagnetic radiation is considered as particle since has mass and carries energy in quanta. Since electromagnetic radiation has mass thus has momentum which can cause ejection of electron in an atom as in photoelectric effect or Compton effect. From quantum physics E = h f……..1 Wave-Particle Duality From Einstein equation of relativity E= mc2…………2 By equating equations 1 and 2 mc2 =hf m=hf/c2 where h is plank’s constant = 6.6×10-34j.s c is speed of light in space =3×108m/s In a unit of kilogram Types of EMR There are two main electromagnetic radiation according to their energy. Ionizing radiation Non- ionizing radiation Ionizing radiation are those radiation with ability to cause ionization of an atom such as X-rays, Gamma rays and Ultra violate radiation. Non-ionizing radiation are those which have no ability to cause ionization of an atom such as radio waves and micro waves. Types of EMR Non-ionizing radiation refers to any type of electromagnetic radiation that does not carry enough energy per quantum to ionize atom or molecules. That is, to completely remove an electron from an atom or molecule. Instead this electromagnetic radiation has sufficient energy only for excitation of electrons (the movement of an electron to a higher energy state.) Uses of EMR Some form of electromagnetic radiation are used in medical purpose such us in diagnosis of diseases on human body and also can be used as therapeutically as in radiotherapy. Such electromagnetic radiation include X-rays, visible light and gamma rays. This electromagnetic radiation have low wave length, high frequency and high energy which allows them to pass through human tissues. The tendency of these wave to pass through human tissue, it help us to diagnose different pathological issues in our body. Visible Light This electromagnetic waves have longer wave length, thus does not penetrate through human tissue But it is useful in diagnosis and treatment procedures since it can be used to guide where the x-rays and gamma rays should be exposed during the diagnostic and therapeutic procedures. Uses of EMR ← PREVIOUS TOPICNEXT TOPIC →VIEW ALL MODULE NOTESVIEW SEMESTER NOTESVIEW ALL LEVEL NOTESALL DIAGNOSTIC RADIOLOGY NOTES Need These Notes as PDF? Need a clean, well-formatted PDF copy for offline study, revision or printing? Request the complete notes directly through WhatsApp. GET WELL-FORMATTED PDF NOTES

DIAGNOSTIC RADIOGRAPHY · NTA LEVEL 4 · SEMESTER ONE Dosimetry Principle CRT04106 · Radiation Sciences START READING NOTES Study Dosimetry Principle using the sections below. Use the topic navigation to continue through Radiation Sciences. Contents of This Topic DOSIMETRY PRINCIPLES IN CALCULATING PATIENT DOSES LEARNING OBJECTIVES Dosimetry DOSIMETER Dosimterer Properties of dosimeters Accuracy and Precision Uncertainty shows the range within which the true value is likely to be, considering errors in the measurement process Characteristics of Dosimeters Ideally, the dosimeter reading M should be linearly proportional to the dosimetric quantity Q. In Fig: Curve A first exhibits linearity with dose, then a supralinear behavior, and finally saturation. Dosimetry Principle Energy response/dependency DIRECTIONAL DEPENDENCE SPATIAL RESOLUTION COMMON DOSIMETERS IONIZATION CHAMBER Types of ionization chamber PARALLEL PLATE CHAMBER (ELECTRON DOSIMETRY) Plane-Parallel Ion Chamber Uses of parallel-plate chamber Extrapolation Chambers How ionization chamber work The movement of these charged particles creates a small electric current that is proportional to the amount of ionizing radiation Function of ionization chamber FILM DOSIMETRY How film dosimeter works Advantages of film dosimeter LUMINESCENCE DOSIMETRY If the exciting agent is light, the phenomena is called OPTICALLY STIMULATED LUMINESCENCE DOSIMETRY (OSD) SEMICONDUCTOR DOSIMETRY HOW SEMICONDUCTOR DIODE WORK TYPES OF SEMICONDUCTOR DOSIMETERS DOSIMETRY PRINCIPLES IN CALCULATING PATIENT DOSES RADIATION SCIENCES LEARNING OBJECTIVES At the end of the session, students should be able to explain: Dosimetry and dosimeter Properties of dosimeters Ionization chamber dosimetry systems Film dosimetry Luminescence dosimetry Semiconductor dosimetry Function of dosimeters Dosimetry Dosimetry is the measurement, calculation and assessment of the ionizing radiation absorbed by an object, usually the human body DOSIMETRY Deals with the measurement of the absorbed dose or dose rate resulting from the interaction of ionizing radiation with matter. -It also refers to the determination of radiologically relevant quantities such as: Exposure Kerma – kinetic energy released in matter Fluence etc DOSIMETER Dosimeter can be defined generally as any device that is capable of providing a reading ‘r’ that is a measure of the absorbed dose ‘D’, deposited in its sensitive volume V by ionizing radiation Dosimterer Dosimeter is a device that measures directly or indirectly Exposure Kerma Absorbed dose Equivalent dose Or other related quantities. The dosimeter along with its reader is referred to as a Dosimetry System. Properties of dosimeters A useful dosimeter exhibits the following properties: High accuracy and precision Linearity of signal with dose over a wide range Dose and dose rate dependence Energy response Small directional dependence High spatial resolution Large dynamic range Accuracy and Precision Accuracy specifies the proximity of the mean value of a measurement to the true value (How a close measurement is to the correct value). Precision specifies the degree of reproducibility of a measurement. The accuracy and precision associated with a measurement is often expressed in terms of its uncertainty. Uncertainty shows the range within which the true value is likely to be, considering errors in the measurement process The standard deviation of the mean value is used to express the uncertainty for the best estimate: Characteristics of Dosimeters Linearity The dosimeter reading should be linearly proportional to the dosimetric quantity. Beyond a certain range, usually there is non linearity. This effect depends on the type of dosimeter. Ideally, the dosimeter reading M should be linearly proportional to the dosimetric quantity Q. However, beyond a certain dose range a non-linearity sets in. The linearity range and the non-linearity behavior depend on the type of dosimeter and its physical characteristics In Fig: Curve A first exhibits linearity with dose, then a supralinear behavior, and finally saturation. Curve B first exhibits linearity and then saturation at high doses In general, a non-linear behavior should be corrected for. A dosimeter and its reader may both exhibit non-linear characteristics, but their combined effect could produce linearity over a wider range Or dose dependence Dosimetry Principle Ideally, the response of a dosimetry system M/Q at two different dose rates ((dQ/dt)1 and (dQ/dt)2) should remain constant. In reality, the dose rate may influence the dosimeter readings and appropriate corrections are necessary, for example: recombination corrections for ionization chambers in pulsed beams Energy response/dependency The response of a dosimetry system M/Q is generally a function of radiation beam quality (energy). Since the dosimetry systems are calibrated at a specified radiation beam quality (or qualities) and used over a much wider energy range, the variation of the response of a dosimetry system with radiation quality (called energy dependence) requires correction. DIRECTIONAL DEPENDENCE The variation in response of a dosimeter with the angle of incidence of radiation is known as the directional, or angular, dependence of the dosimeter. Dosimeters usually exhibit directional dependence, due to their constructional details, physical size and the energy of the incident radiation. Dosimetry Principle Directional dependence is important in certain applications, for example in in vivo dosimetry while using semiconductor dosimeters. Therapy dosimeters are generally used in the same geometry as that in which they are calibrated. SPATIAL RESOLUTION The quantity absorbed dose is a point of quantity Ideal measurement requires a point-like detector Measurement result can be attributed to a point within the volume referred to as the effective point of measurement COMMON DOSIMETERS Ionization chamber Film dosimeter Luminescence dosimeter Semiconductor IONIZATION CHAMBER Are-gas filled spaces between two electrodes, typically parallel plates or a hollow cylinder and a thin wire They operate at a saturation voltage, and the current passing through them can be recorded by a voltmeter Types of ionization chamber Free air ionization chamber Thimble ionization chamber Plane-parallel ionization chamber Well-type chamber Pocket ionization chamber Extrapolation ionization chamber Geiger-Muller counter Proportional counter Ionization Chamber Cylindrical (thimble) ionization chamber Most popular design Independent of radial beam direction Typical volume between 0.05 -1.00 cm3 Typical radius ~2-7 mm Length~ 4-25 mm Thin walls: ~0.1 g/cm2 Used for: electron, photon, proton, or ion beams. Thimble Chamber PARALLEL PLATE CHAMBER (ELECTRON DOSIMETRY) Consist of two plane walls, one serving as an entry window and polarizing electrode and the other as the black wall and collecting electrode, as well as